Because we have television data that span a number of elections, we can provide detailed information on how prominent TV ads are overall or in any given location, how many different types of sponsors are active and how the content of advertising compares to prior election cycles.

Of course, television is not the only medium through which campaigns attempt to reach voters. But online advertising, which represents the biggest growth market, has been much harder to track.

What role did political advertising play in the 2018 midterm elections? Here are our top observations:

1. Digital advertising grew in 2018.

Data on digital ads in prior cycles are not readily available, but we know from campaigns and practitioners that the dollars spent in online advertising are growing quickly. Facebook reports that just under US$400 million was spent on its platform for political ads, ranging from U.S. Senate races to county sheriff, between May of 2018 and Election Day.

Google reports about $70 million in spending on ads in races for the U.S. Senate and House on its ad network during a comparable time period.

Some candidates prioritized digital advertising over traditional television ads. For example, Texas Senate candidate Beto O’Rourke spent at least $8 million on Facebook and another $2 million on Google. That was about 34 percent of the $29.4 million total that his campaign spent on advertising, if we include the $19.4 million spent on broadcast television in 2018.

To be sure, O’Rourke was an outlier. We found in October that about 10 percent of spending by Senate candidates on advertising was on digital ads between May 31 and Oct. 15, 2018.

Still – in a fragmenting media environment where people receive information from a variety of different sources and spend substantial time on social media and online – you might assume that campaigns’ heavy focus on digital advertising would displace television advertising.

Nothing could be further from the truth.

2. TV is still important to congressional and statewide campaigns.

This is demonstrated by the record number of television ads in 2018. Data from our project show that the number of ads aired in races for governor, U.S. Senate and U.S. House increased by 58 percent from 2014 to 2018, from 2.5 million to almost 4 million ad airings.

The biggest increase was in U.S. House races, where ad airings rose from under 600,000 in 2014 to over 1.2 million in 2018. The large number of competitive races in 2018, especially in the U.S. House, may account for much of the increase.

3. The election was about health care.

Even in a fragmented media era with a hyper-polarized electorate, advertising in 2018 shows that it is still possible to find agreement across campaigns on the importance of particular issues.

In this cycle, that issue was clearly health care.

More than a third of the record-breaking number of ads aired in federal and gubernatorial races mentioned health care, and the attention to health care as an issue only grew throughout the cycle, with 41.4 percent of all airings in the post-Labor Day period mentioning the issue. In total, 1.4 million airings mentioned health care and 979,249 of those aired between Sept. 4 and Election Day. Health care was by far the most mentioned issue.

The dominance of health care was driven by the laser focus on the issue on the Democratic side. A little more than half of pro-Democratic ads in federal races during the post-Labor Day period mentioned the topic. By contrast, the second largest issue was taxes, at 14.7 percent of airings.

Although pro-Republican airings in federal races talked more about taxes during this window – 35.3 percent – than any other issue, health care ran a close second, appearing in nearly a third of pro-Republican airings.

Pro-Democratic gubernatorial airings also talked more about health care – 45.5 percent – than any other single issue. Education and taxes ranked second and third, respectively.

Pro-Republican gubernatorial airings were the only ones that did not include health care in the top two topics, but the issue did rank fifth in percentage of airings in the post-Labor Day period. It was behind taxes, education, jobs and public safety issues.

4. Outside groups continue to be active.

Outside groups paid for 22 percent of ads aired in U.S. House races in 2018, an increase over the 15 percent of group airings in 2016. And those outside groups paid for a little more than one-third of all ads aired in U.S. Senate races, a slight decrease from 2016.

In partnership with the Center for Responsive Politics, we categorize these groups into three classifications: full-disclosure groups, meaning they disclose contributor lists to the Federal Election Commission; nondisclosing dark money groups that are most often 501(c)4 nonprofits; and partial-disclosure groups that identify donors but also accept contributions from dark money sources.

In past cycles, we found that dark money was more prevalent among Republican groups than pro-Democratic ones. This cycle, the pattern flipped.

One in four, or 25 percent, of ads aired by groups on behalf of Democratic House candidates in the election year was from a dark money group. Only about 12 percent of pro-Republican ads aired by groups in House races was from a dark money sponsor.

In Senate races, dark money sponsors for Democrats and Republicans were about equal in share, roughly one in every three outside group ads on either side of the aisle.

Nowhere to hide

All told, 2018 was a “do everything” election, where many campaigns invested heavily in traditional TV ads and online advertising facilitated by social media.

We have long suspected that TV ads would decline as digital ascended. That may yet happen, but in 2018 voters were truly bombarded by ads on their TV screens.

Political ads may have stopped for the moment, but the reprieve will be brief.

Our data show that election off-years, as 2019 is, will still feature substantial amounts of campaign advertising, often reminding voters about accomplishments in office or setting up attacks on vulnerable incumbents.